1. Field of the Invention
The present invention relates to a recording apparatus (particularly a printer head) configured of a transfer portion for holding recording material and a resistance heating means for heating the recording material such that the recording material is caused to fly, thereby transferring onto a recording medium disposed opposing the transfer portion, and also relates to a method for manufacturing the recording apparatus.
2. Description of the Related Art
In recent years, a field has emerged wherein color images processed with personal computers or the like, or color images taken with video cameras or electronic still photography cameras are printed out, and used for viewing enjoyment or other purposes. Accordingly, there are increasing needs for printers which provide high-quality full-color images, and particularly for personal-use printers or relatively inexpensive printers geared for small-scale businesses (so-called "small-office" "home-office" businesses) which provide such high-quality full-color images.
Color printing methods which have been proposed include the sublimation-type thermal transfer method (or dye dispersion thermal transfer method), the melt thermal transfer method, the ink-jet method, the electro-photography method, the thermal-developing silver-salt method, and so forth. Of these, the dye dispersion thermal transfer method and ink-jet method can be listed as examples of methods whereby high-quality images can be easily output from relatively simple devices.
The dye dispersion thermal transfer method uses an ink ribbon or sheet coated with an ink layer formed by dispersing a high concentration of transfer dye within an appropriate binder resin, and so-called thermal transfer sheets which are formed by coating paper with dyeing resin which accepts the transferred dye. The ink ribbon or sheet is pressed against the thermal transfer sheet at a certain pressure, and a thermo-sensitive recording head (thermal head) applies heat from behind the ink ribbon or sheet, thus performing thermal transfer of transfer dye from the ink ribbon or sheet to the thermal transfer sheet, the amount of transfer dye being transferred according to the amount of heat.
A full-color image with continuous gradation can be obtained by repeating this operation for image signals resolved into the three primary colors of subtractive color mixture, i.e., yellow (Y), magenta (M), and cyan (C).
FIG. 26 shows the configuration of the area surrounding a thermal head of a printer using this dye dispersion thermal transfer method.
A thermal head 70 is positioned so as to oppose a platen roller 77, and an ink sheet 72 which has been formed by providing an ink layer 73 on a base film 71, for example, along with a recording sheet (thermal transfer paper) 75 formed by coating the surface of paper 76 with a dying resin layer (dye-accepting layer) 74, run in the direction of the arrow B in the Figure while being pressed against the thermal head 70 by the platen roller 77 which rotates in the direction of the arrow A in the Figure.
Then, the ink in the ink layer 73 selectively heated by the thermal head 70 according to the image to be printed is subjected to thermal dispersion into the dying resin layer 74 of the recording sheet 75 which has been heated by coming into contact with the ink layer 73, and transfer is carried out by dot pattern, for example.
This dye dispersion thermal transfer method is an excellent technique in that the printer can be reduced in size and maintenance thereof is simple, the printer has immediate availability, and images with quality rivaling that of silver-salt color photography can be obtained. However, this method is problematic in that disposal of the ink ribbon or sheet results in massive amounts of discarded materials and high running costs. This method also necessitates the use of thermal transfer sheets, which also raises running costs.
The melt thermal transfer method can be used with plain paper, but still uses ink ribbon or sheet, and so this method is also problematic in that the disposal of such results in massive amounts of discarded materials and high running costs. Further, the image quality is lower than that of silver-salt color photography.
The thermal developing silver-salt method is high in image quality, but necessitates use of dedicated photographic printing paper and throw-away ink ribbon or sheets, so running costs are high, and further, the apparatus itself is expensive.
On the other hand, the ink-jet method is a method wherein droplets of ink are discharged from nozzles provided to a printer head, using methods such as electrostatic gravity, continuous vibration generation (piezo method), thermal (bubble-jet method), and the like, as described in Japanese Patent Publication No. 61-59911, Japanese Patent Publication No. 5-217, and so forth, whereby the droplets of ink adhere to the printing paper or the like, thereby conducting printing.
Accordingly, printing can be performed in plain paper, and ink ribbons or the like are not used, so running costs are low, and there are hardly any discarded items generated as with the case of using ink ribbons or the like. This method is becoming widespread in recent years, since color images can be easily printed.
However, the principle of the ink-jet method makes concentration gradients in pixels difficult, and it has been difficult to realize images with quality rivaling that of silver-salt color photography in a short time, as can be with the above-described dye dispersion thermal transfer method. That is to say, with the known ink-jet method, one droplet forms one pixel, so this principle makes concentration gradients within pixels difficult, and accordingly, high-quality images could not be realized. Also, pseudo-gradient representations with dithering using the high resolution of ink jets is being attempted, but image quality equal to that of the dye dispersion thermal transfer method has not been obtained, and moreover, the transfer speed drastically drops when employing such methods.
Recently, ink-jet methods which use thinned ink to obtain two or three gradients within a pixel are emerging, but it has been difficult to obtain image quality equal to that of silver-salt photography or dye dispersion thermal transfer methods, particularly with natural images or the like.
As for the electro-photography method, the running cost is low and transfer speed is high, but not only does the image quality not rival that of silver-salt photography, but the equipment is markedly expensive.
To summarize the above, none of these recording methods have satisfied all of the demands of image quality, running costs, equipment costs, transfer time, and so forth.
Hence, the so-called dye vaporization thermal transfer method (e.g., Japanese Unexamined Patent Publication No. 9-183239) has been proposed as a color printing method capable of satisfying all of the above demands.
Now, the structure surrounding the transfer portion near the tip of a printer head according to the known dye vaporization thermal transfer method will be described with reference to FIG. 27 and FIG. 28. Incidentally, FIG. 28 is an exploded cross-sectional view along line XXVIII--XXVIII in FIG. 27.
As shown in FIG. 28, this printer head (heater chip) 92 has a layered structure wherein, for example, a high-resistance poly-silicone film 82 serving as a heater (heat-generating element) is formed on a substrate 80 formed of silicone, via a silicone oxide (SiO.sub.2) film 81. In the event that a thermal insulating substrate such as a quartz plate is to be used for the substrate 80, the high-resistance poly-silicone film serving as the heater can be directly formed on the substrate without a thermo-insulating layer such as the SiO.sub.2 film 81.
Further, formed upon this poly-silicone film 82 are an individual electrode 83 and common electrode 84 formed of aluminum (Al) wiring patterning. Provided to the transfer portion 89 defined by the partition 86 and accessory wall 87 is a rough ink holding structure, this being formed of a great number of post-like members 88 having a width or diameter of around 2 .mu.m and a height of around 6 .mu.m being erected so as to leave minute gaps therebetween of around 2 .mu.m.
FIG. 27 is a plan drawing of the portion around the transfer portion 89. As shown in FIG. 28, the poly-silicone film 82 serving as the heater is also formed under the electrodes 83 and 84, so the poly-silicone film 82 serves as a part of the wiring at the portions where the electrodes 83 and 84 exist, and serves as a resistance-heating heater 91 at the portions where the electrodes 83 and 84 do not exist thereupon.
Then, with a printer head upon which a plurality of transfer portions of such a configuration are arrayed, the heater 91 selected by the common electrode 84 and individual electrode 83 according to the image information to be printed is heated, ink (not shown in the diagram) supplied to the transfer portion (vaporizing unit) 89 from the ink supplying channel 90 defined by the accessory wall 87 and partition 86 in a spontaneous manner by capillary phenomena flies, thus being transferred onto a recording medium such as paper.
The above-described dye vaporization thermal transfer method consists of heating ink at the transfer portion of a printer head, causing the ink to fly by means of vaporization ablation, capillary waves, etc., by which the ink is caused to adhere to the surface of a recording medium (photographic printing paper) such as printer paper positioned so as to oppose the printer head across a gap of around 50 to 100 .mu.m for example, thereby performing the transfer.
Also, as described above, provided to the transfer portion is a rough ink holding structure formed of a great number of post-like members having a width or diameter of around 2 .mu.m and a height of around 6 .mu.m being erected so as to leave minute gaps therebetween of around 2 .mu.m, and a heater is provided below this ink holding structure, thus making up the vaporizing portion (transfer portion).
Providing the transfer portion with such an ink holding structure yields the following advantages (1) through (4):
(1) Ink is supplied to the vaporizing portion in a spontaneous manner by capillary phenomena.
(2) Ink can be effectively heated, due to the great surface area.
(3) Setting the height of the post-like members to an appropriate height allows a certain amount of ink to be held in the vaporizing portion at all times.
(4) The surface tension of liquid generally has negative temperature coefficients, so locally heated ink receives force toward the perimeter where the temperature is lower, but such movement can be suppressed to a minimum due to the ink holding structure, and deterioration of transfer sensitivity tends to be prevented.
Accordingly, an amount of ink according to the amount of heating by the vaporizing portion can be caused to fly, and to be transferred into the printer paper or the like, meaning that continuous control of the amount of ink transferred can be realized, i.e., gradation of concentration within a pixel can be realized. consequently, high-quality images rivaling that of silver-salt color photography can be obtained.
Also, there is no need to use an ink ribbon or the like, so running costs are low, and further, plain paper transfer can be realized by using ink which has high absorption properties with plain paper, which also can lower costs.
Also, this method takes advantage of vaporization, ablation, etc., of the ink, i.e., of the dye, so the transfer portion of the printer head which heats the ink does not need to be brought into contact with the recording medium such a printing paper, much less pressed against it at high pressure. Accordingly, the problem of thermal fusion between the portion for heating the ink such as the ink ribbon and the printer paper and the like, which could occasionally occur with other thermal transfer methods.
However, careful study by the present Inventor has shown that there is room for improvement with this known dye vaporization thermal transfer method printer.
That is, with this dye vaporization thermal transfer method printer in particular, one printer head contains a plurality of transfer portions (portions for causing ink to fly, or vaporizing portions; the term "transfer portion" will hereafter be understood to indicate such) in one or multiple columns as described above, and each heater generates heat according to the image information by the so-called resistance heating method, thus controlling the amount of ink transferred to the recording medium.
Accordingly, in the event that there are irregularities in the resistance values of each of the heat generating elements (heaters, resistance heating means or low-resistance portions; the term "heat generating element" will hereafter be understood to indicate such) provided to the multiple transfer portions, the amount of heat from Joule heat generates deviations for the same image information, which appear as irregularities in concentration within the transferred image. With the conventional structure for heat generating elements, the irregularities in resistance values within each of the heat generating elements could not be precisely controlled, resulting in deterioration in image quality.
This is due to the fact that aluminum, which is the principal component of the electrodes easily disperses into the poly-silicone which is the principal component of the heater, and dispersion of the aluminum into the poly-silicone occurs at the interface between the heater portion where no electrodes exist on the poly-silicone and the aluminum, owing to heat processing in the manufacturing processes such as the electrode formation step, or owing to own heat generated from the resistance heating means at the time of driving the recording apparatus, and further, the degree of dispersion differs from one heater to the next in the transfer portions, so there is the deviation of resistance values between the heaters. This will be described in further detail later.
In other words, in the event that the structure around the transfer portion is a configuration such as shown in FIG. 27 and FIG. 28, the resistance value of the heat generating element tends to shift to a value which is different from the desired value regarding the same image information, either at the process of manufacturing or over time, thus creating differences in the amount of heat generated by the heaters, resulting in irregularities in transfer concentration.